Danfoss FC 300 Design Manual

Also see for FC 300: Operating instructions Instruction manual Design guide Design guide Design guide

Contents

Danfoss FC 300 Design Manual Manual pdf 42 page image

NB!Do not touch the brake resistor as itcan get very hot while/after braking.Control with Brake FunctionThe brake is to limit the voltage in the intermediate circuit when the motor acts as a generator. Thisoccurs, for example, when the load drives the motor and the power accumulates on the DC link. Thebrake is built up as a chopper circuit with the connection of an external brake resistor. Placing the brakeresistor externally offers the following advantages:- The brake resistor can be selected on the basis of the application in question.- The brake energy can be dissipated outside the control panel, i.e. where the energy can be uti-lized.- The electronics of the frequency converter will not be overheated if the brake resistor is over-loaded.The brake is protected against short-circuiting of the brake resistor, and the brake transistor is monitoredto ensure that short-circuiting of the transistor is detected. A relay/digital output can be used for pro-tecting the brake resistor against overloading in connection with a fault in the frequency converter.In addition, the brake makes it possible to read out the momentary power and the mean power for thelatest 120 seconds. The brake can also monitor the power energizing and make sure it does not exceeda limit selected in par. 2-12. In par. 2-13, select the function to carry out when the power transmittedto the brake resistor exceeds the limit set in par. 2-12.NB!Monitoring the brake power is not a safety function; a thermal switch is required for thatpurpose. The brake resistor circuit is not earth leakage protected.Over voltage control (OVC) (exclusive brake resistor) can be selected as an alternative brake function inpar. 2-17. This function is active for all units. The function ensures that a trip can be avoided if the DClink voltage increases. This is done by increasing the output frequency to limit the voltage from the DClink. It is a very useful function, e.g. if the ramp-down time is too short since tripping of the frequencyconverter is avoided. In this situation the ramp-down time is extended.Control of Mechanical BrakeFor hoisting applications, it is necessary to be able to control an electro-magnetic brake. For controllingthe brake, a relay output (relay1 or relay2) or a programmed digital output (terminal 27 or 29) is re-quired. Normally, this output must be closed for as long as the frequency converter is unable to íholdíthe motor, e.g. because of too big load. In par. 5-40 (Array parameter), par. 5-30, or par. 5-31 (digitaloutput 27 or 29), select mechanical brake control [32] for applications with an electro-magnetic brake.When mechanical brake control [32] is selected, the mechanical brake relay stays closed during startuntil the output current is above the level selected in par. 2-20 Release Brake Current. During stop, themechanical brake will close when the speed is below the level selected in par. 2-21 Activate Brake Speed[RPM]. If the frequency converter is brought into an alarm condition, i.e. over-voltage situation, the me-chanical brake immediately cuts in. This is also the case during safe stop.FC 300 Design GuideIntroduction to FC 30042 MG.33.B7.02 - VLT is a registered Danfoss trademark